a) Field of the Invention
The present invention relates to a thin film magnetic head for recording or reproducing data in or from a magnetic recording medium, the thin film magnetic head being of the type that a magnetic path is formed between upper and lower magnetic core layers of upper and lower poles with a gap layer being interposed therebetween.
b) Description of the Related Art
An example of conventional thin film magnetic heads is described, for example, in JP-A-4-356704 (now issued as U.S. Pat. No. 5,479,310). FIGS. 26, 27, and 28 illustrate a conventional manufacture method of a thin film magnetic head. FIG. 28 is a plan view, FIG. 26 is a cross sectional view showing a magnetic core in a longitudinal direction taken along line A--A of FIG. 28, and FIG. 27 is a cross sectional view of the magnetic core in a width direction taken along line B--B of FIG. 28. As shown in FIG. 26, an insulating layer 1 is formed on a substrate and a lower magnetic core-layer 2 is formed on the surface of the insulating layer 1. On the lower magnetic core layer 2, a magnetic gap layer 3 is formed. A plurality of coil layers 5 embedded in an insulating layer 4 is formed on the magnetic gap layer 3. A resist layer 6 is formed over the whole surface of the substrate, covering the insulating layer 4.
This resist layer 6 is patterned through exposure and development to form an opening 7 to be used for the formation of an upper magnetic core layer and an upper pole. The upper pole is formed at the tip portion 8 of the opening 7. In this tip portion, magnetic material such as 81-permalloy is embedded and the patterned resist layer 6 is removed to form the upper magnetic core and upper pole.
With this conventional manufacture method of a thin film magnetic head, however, the cross section of the tip portion 8 of the patterned resist layer 6 is wider at the upper area and narrower at the lower area, as shown in FIG. 27, and it is difficult to control the width of the upper pole and the widths of upper poles easily vary. The reason for this is as follows. The insulating layer 4 with the coil layers 5 being embedded has a bulky pattern with a thickness of 10 to 20 .mu.m. In order to sufficiently cover this bulky pattern, the resist layer 6 for the formation of the upper magnetic core layer and upper pole is required to be deposited very thick. The resist pattern 6, particularly at the upper pole forming portion (tip portion), becomes thicker to 7 to 15 .mu.m. If an upper pole pattern of 4 .mu.m wide or less is formed after exposure and development of such a thick resist layer 6, its width is very unstable and varies. A precision 3.sigma. of the pole width is therefore +/-0.7 .mu.m at the best. Such a large variation is not adequate for a thin film magnetic head to be used with a hard disk of narrow track and high density record.
Instead of 81-permalloy (81 Ni-19 Fe: by an weight ratio, the same notation is used in the following), magnetic material of high saturation magnetic flux density may be used as the material of the pole to apply dense magnetic fluxes to a magnetic recording medium. In this case, the magnetic flux density at the gap side of the pole becomes high and its slope becomes sharp, so that a strong signal can be written in a high performance recording medium with a high magnetic coercive force (Hc). The magnetization inversion transition area of a recording medium becomes narrow and sharp so that NLTS (nonlinear transition shift, also called NLBS (nonlinear bit shift)) is improved and a record density can be increased.
For example, as compared to a saturation magnetic flux density (Bs) of about 8000 G of 81-permalloy (81 Ni-19 Fe), Bs is about 16000 G for the high saturation magnetic flux density material such as 94 Co-6 Fe, 45 Ni-55 Fe, and FeTaN, and is about 15500 G for 30 Fe-25 Co-45 Ni. Such materials having saturation magnetic flux density higher than that of 81-permalloy may be used as the pole material in order to increase the record density.
Since the upper magnetic core layer and upper pole of a conventional thin film magnetic head are formed after a single photolithography process, both the upper magnetic core layer and upper pole are formed by the same material of high saturation magnetic flux density. Since the magnetostrictive coefficient .pi.s of the high saturation magnetic flux density material is larger than 81-permalloy, if strains are formed in the core by its internal stress or thermal stress, the magnetic characteristics of material of high saturation magnetic flux density change greatly and are degraded. The upper magnetic core layer is susceptible to stresses and has a relatively large area. Therefore, if strains are generated in the upper magnetic core layer made of material of high saturation magnetic flux density, by internal stress or thermal stress, the magnetic core layer and the whole magnetic path are influenced greatly, being unable to obtain stable magnetic characteristics.